-na (4), ending used to form passive participles as well as some adjectives and nouns; see -ina. According to PE17:68, the ending -na was "no longer part of verbal conjugation"; the derived words are thus considered independent adjectives (sometimes nouns) rather than regularly derived passive participles, the obvious etymological connection to certain verbal stems notwithstanding. Where adding the ending to a root would produce the combinations tn, pn, kn (cn), metathesis occurs to produce nt, (np >) mp, nc, as in nanca *"slain" for older ¤ndakna, or hampa "restrained, delayed, kept" vs. the root KHAP "retain, keep, detain". Following -l, the suffix -na turns into -da, as in yulda "draught, the amount drunk" for older yulna (this being an example of a noun being derived with this ending, though Tolkien might also explain yulda as containing a distinct ending -da [q.v.] denoting the result of a verbal action). The word *turúna "mastered" (q.v., only attested in elided form turún) would seem to be a passive participle formed from the verb turu- "master" (PE17:113), suggesting that in the case of U-stem verbs, their final -u is lengthened to ú when -na is added.
Quenya
hampa
restrained, delayed, kept
hampa
adjective. restrained, delayed, kept
-na
no longer part of verbal conjugation
hampa adj. "restrained, delayed, kept" (PE17:68)